Document transport for photocopy machine



Nov. 7, 1967 F. R. LEVINE 3,351,340

DOCUMENT TRANSPORT FOR PHOTOCOPY MACHINE. Fil ed June so. 1964 3Sheets-Sheet 1 INVENTORI FRANKLIN R. Levms a 144%, 7%, VJwwM I Ar'rvs.

1967 F. R. LEVINE DOCUMENT TRANSPORT FOR PHOTOCOPY MACHINE 5Sheets-Sheet Z Filed June 30. 1964 INVENTOR I FRANKLIN R. LEVINE W4,Mad, vJwM Nov. 7, 1967 F. R. LEVINE 3,351,340

DOCUMENT TRANSPORT FOR PHOTOCOPY MACHINE Filed June so. 19643Sheets-Sheet 5 LL FRANKLIN E. Lev/us 6 n &%MM, 4/J zaw m A'rrvs.

United States Patent C 3,351,340 DOCUMENT TRANSPORT FOR PHOTOCOPYMACHINE Franklin R. Levine, Elk Grove Village, 11]., assignor toAmerican Photocopy Equipment Company, Evanston,

11]., a corporation of Illinois Filed June 30, 1964, Ser. No. 379,205 9Claims. (Cl. 271-51) The present invention relates to an officephotocopy machine and more particularly to means for transporting theoriginal document in a machine of this type.

In the copending Kent and Levine application Ser. No. 364,698, filed May4, 1964, entitled Electrostatic Photocopy Machine, and assigned to theassignee of the present application now Patent No. 3,303,763, means areprovided for applying an electrostatic charge to an original document asit is brought into engagement with a transport drum to produce adherenceof the original to the drum surface by electrostatic attraction. Severalcharging devices are positioned about the drum periphery forreplenishing the charge on the original thereby to compensate forleakage of charge into the drum; alternatively, the drum may be coveredwith an insulating blanket of plastic or the like to minimize leakage.Where an insulating blanket is used there is a tendency for a charge ofthe applied polarity to be built up on the surface of the insulatingblanket as a result of repeated exposure and, since such charge is ofthe same polarity as that applied to the face of the original, theefiect is to lessen the electrostatic attraction between the originaland the drum. Where the original is of heavy gauge, stifi? material as,for example, Bristol board, there is risk that the leading edge of theoriginal may spring free of the drum under certain conditions, forexample, high humidity.

It is, accordingly, an object of the present invention to provide aphotocopy machine having improved electrostatic means for securelyholding and transporting the original through the machine. It is anotherobject to provide a photocopy machine in which electrostatic forces areemployed to hold an original document on an insulated transportingsurface but which prevents the building up of any charges which mighttend to neutralize the attractive forces as a result of repeatedexposure to a corona unit or similar charging device. It is, on thecontrary, an object of the invention to :provide a transportingarrangement for an original document in which there is applied to theface of the document, and in lesser degree to the supporting surface, anelectric charge of a first polarity followed a short time later by asecond charge of opposite polarity thereby to preclude any cumulativebuildup of charge as a result of repeated cycling.

It is a further object to provide a photocopy machine having a drum towhich an original document adheres by electrostatic attraction and whichincludes means for pre-curling the original document to the shape of thedrum just prior to contact with the drum to reduce the possibility ofthe leading or trailing edges of the original springing free of the drumbecause of the usual tendency of an original to restore itself to a flatcondition. More specifically, it is an object, in a machine of thistype, to provide a set of curling members for curling an original,particularly one of a stiff or spingy nature, beyond its elastic limitjust prior to depositing the original on the drum so that the originaltends to cling to the drum with only minor reliance on electrostaticforce and so that the original tends to maintain the contour of the drumeven in the temporary absence of electrostatic force, as, for example,when the machine is inadvertently turned off before the original hasbeen discharged. Thus, it is an object of the invention to provide aphotocopy ma- 3,351,340 Patented Nov. 7, 1967 chine in whichelectrostatic forces are efiiciently utilized to prevent creeping orskewing of the original and which is reliable and substantiallyjam-proof under all conditions including wide variations in humidity,wide variations in the nature of the original, and wide variations inthe voltage of the electrostatc charge.

It is an object of the present invention in one of its aspects toprovide a photocopy machine having a cylindrical path of transport withmeans for pre-curling the original so that it conforms snugly to thetransport surface during the transporting and exposing cycle incombination with means for uncurling the original as a final step sothat the original leaves the machine in substantially flat condition.

It is in general an object of the invention to provide a photocopymachine having means for securely holding and transporting the originalby electrostatic forces but which is nevertheless simple and efficientproducing improved adhesion and improved reliability without necessityfor resorting to higher charging voltages, and which may, indeed, permita reduction in voltage. Finally, it is an object of the invention toprovide a photocopy machine of the electrostatic type which in spite ofits improved -features may be constructed more compactly and at lesscost than competitive photocopy machines.

Other objects and advantages will become apparent upon reading theattached detailed description and upon reference to the drawings inwhich:

FIGURE 1 is a perspective view, on a reduced scale, of a photocopymachine employing the features of the present invention;

FIG. 2 is a vertical section taken through the machine of FIG. 1;

FIG. 2a is a fragmentary section taken through the periphery of thetransport drum;

FIG. 3 is a schematic diagram showing the driving means for driving thetransport members in FIG. 2;

FIG. 4 is a simplified diagram of the control circuit;

FIG. 5 is a diagram showing the charging circuits;

FIG. 6 is a fragmentary stop motion view showing the electrostaticcharging at the leading edge portion of the original as the original ispassed into the first charging unit;

FIG. 7 is a stop motion view similar to FIG. 6 but showing the reversalof electrostatic charge as the original s passed into the secondcharging unit;

FIG. 8 is a diagram showing the precurling rollers and the set imposedupon an original of stiff springy material, such as Bristol board, fortransport through the machine;

FIG. 9 is a fragmentary view of the original-discharging portion of themachine of FIG. 2 showing an alternate roller arrangement for restoringa curved original back into substantially flat condition and showing useof an auxiliary grounded electrode for removing any residual charge fromthe transport surface; and

FIG. 10 is a schematic diagram of an alternate charging arrangement inwhich switching means are provided for applying the voltage of first andsecond polarity to the face of the original While the invention has beendescribed in connection with certain preferred embodiments, it will beunderstood that I do not intend to be limited to the particularembodiments illustrated but intend to cover the various alternative andequivalent arrangements included within the spirit and scope of theappended claims.

Turning now to the drawings there is shown in FIG. 1 a machine 10constructed in accordance with the invention and suitable for ofiiceuse. The machine includes a Work table 11 having an entry slot 12 forfeeding original documents into the machine together with lateral guides13 which are adjustable in width and which serve to aline and center theoriginal. Upon completion of the photocopy process, the original isdischarged into a tray 15 which is included within the confines of thehousing and which is readily accessible from the front of the machine.The completed copies collect in a lower tray 16. The machine is put intooperation by an on-off switch 17 having an associated pilot light 18 andwith a control button 19 which may be actuated where a number of copiesof the original are desired.

For the purpose of gripping the leading edge of an original 20 which isplaced upon the table 11 face up, a pair of resilient nipping rollers21, 22 (FIG. 2) are provided communicating with a pair of guides 23. Thelatter feed the original to a feed roller assembly 25 consisting of adriven roller 26 and idler rollers 27, 28 which deposit the original ona transport drum 30 having an outer surface 31 and which is journaled inthe frame in bearings 32. For the purpose of causing the original toadhere to the drum, a first corona unit 33 is provided having chargedwires 34 and, spaced therefrom, about the periphery of the drum, asecond corona unit 35 is provided having charged wires 36 connected to asoure of high voltage.

The original, adhering to the drum, passes into an illuminating station40 having light sources 41 with light shields 42, respectively, whichform the lower and upper edges of a slot 43 which defines the readingarea on the drum. The lamps 41 are preferably of the fluorescent typeextending the length of the drum and are, as shown, located closelyadjacent the drum surface to provide a high level of illumination atrelatively low wattage. For the purpose of stripping off the originalfrom the drum a stripper is used which may extend the width of the drumand which has a shaft 44 from which project a series of alined fingers45. A linkage 46 couples the shaft to the control knob 19. A spring 47may be provided to bias the stripper in the direction of the drumnormally producing a single copy. The drum is formed with a series ofgrooves 30a (FIG. 2a) defining fiat-topped ridges with the fingersregistering in the grooves. After passing the illuminating station theoriginal is directed upwardly into the nip of a pair of expellerrollers. This function is performed in the present instance by theroller 22 previously referred to and an adjacent roller 48 which directsthe original between a pair of guides 49 and thence onto the originalreceiving tray.

When multiple copies are desired, the knob 19 may be pulled therebylifting the stripper from the drum and permitting the original torecirculate as often as may be desired. The control panel at the frontof the machine may be equipped with a tally device to serve as a visualindication to the operator of the number of times that the drum isrotated with the same original.

Turning attention next to the lower portion of the machine, means areprovided for storing a stack of photocopy sheets and for feeding thesheets one by one by a separate feed motor which is controlled bycircuitry to be discussed at a later point. For the details ofconstruction of the feed motor and the associated feed elements,reference is made to Sacre US. Patent 3,126,122 which issued on Mar. 24,1964. Briefly stated, a stack of copy sheets 50 is provided, with a topsheet 51. In engagement with the top sheet is a rubber drive roller 52which presses, by gravity or spring pressure, against the sheets andwhich is journaled in a pair of arms 53. The feed roller 52 is driven bya motor 55 with gears 56 completing the drive connection.

When the feed motor 55 is turned on, the top sheet 51 is driven througha pair of spaced guides 57 into a ready. position 58. From this positionthe sheet is transported, by further energization of the motor 55, intoengagement with copy sheet transport means including a pair of niprollers 61, 62 and a pair of transport rollers 63, 64 joined by a pairof arcuate guides 65. As will be discussed,

drive means are provided for rotating the nip and transport rollers at aspeed which corresponds to the peripheral speed of the original drum 39.

For the purpose of imparting an electrical charge to the front and backsurfaces of the copy sheet, the sheet passes through a charging station70 formed of opposed corona units 71, 72, having wires 73, 74 which arecharged with voltage of opposite polarity by a high voltage supply 75.The copy sheet is guided between the corona units by insulating cords ofnylon or the like which are strung across the open faces of the units.-

From the charging station 70 the copy sheet is immedi- In the presentinstance, the development takes place in a developing tank 90 havingguiding edges 91 which engage the back of the sheet and which serve todirect the sheet through a body of developer fluid 92. The developerfluid is preferably a dielectric liquid having distributed therein acolloidal suspension of pigmented particles or toner which tend toadhere to the charged areas of the copy sheet thereby to develop thelatent image acquired at the exposing station. From the developing tank90 the sheet passes between a pair of expeller or squeegee rollers 95,96, which are resiliently surfaced and biased together so that excessliquid runs back to the tank 90. From the rollers 95, 96 the sheetpasses into a pair of guides 97 from which the sheet is discharged intothe copy tray 16 previously referred to.

For the purpose of rotating the drum 30 and the transport rollers at thesame peripheral speed, they are interconnected by rubber timing beltscommonly referred to as cog belts or the like. Thus, the drive motor100, which is preferably geared down to an output speed on the order of20 r.p.m., has a first belt 101 (FIG. 3) which is trained abouttransport rollers 22, 26, 61 and 95, and a second belt 102 which istrained about the drum 30, transport roller 63, idler pulley 103 androller 89. The rollers not directly engaged by the belts are driven byrolling friction.

It will be understood, of course, that the driving arrangement indicatedat FIG. 3 is simply exemplary and that other specific beltconfigurations may be used without departing from the present invention.

For the purpose of casting the image of the original upon the copy sheetwith both original and copy sheet moving in unison, an opticalreflecting element 110 is used having a lens 111 and a mirror 112. Theoptical system is shielded against ambient light by a suitable opticalhousing 113, the optical path between the illuminating station andexposing station being indicated at 114. The light housing is preferablypyramidal or trapezoidal in cross section to conform approximately tothe optical path and to define upper and lower spaces 115, 116 for thetrays 15, 16, previouslyreferred to.

For the purpose of understanding the control circuit which controls thetransport and phasing of the copy sheet with respect to the original, acontrol arrangement is used which is set forth in simplified form inFIG. 4. The current is taken from a pair of supply lines 121, 122, sothat, when the on-ofl switch 17 is closed, the lamps 41, the highvoltage supply 75, and main drive motor are energized as confirmed bythe lighting of the pilot light 18.

To advance a copy sheet to the ready position 58, a normally closedswitch is used (FIGS. 2 and 4) having a feeler finger 131 located at theready position and connected in series with the copy sheet drive motor55.

spaced the stack and which upon arrival at the ready position turns offthe motor. For the purpose of additionally energizing the motor 55 forfeeding of the copy sheet into the transport means in synchronism withthe feeding of the original, a normally open switch 133 (FIG. 2) havinga feeler finger 134 is provided in the path of movement of the original.The feeler finger 134 extends into one of the grooves 30a. Thus uponarrival of the leading edge of the original the switch 133 is closed,energizing the drive motor 55 so that the copy sheet is advanced intoengagement with the nip rollers 61, 62 which then take over to advancethe sheet through the guides 65 and transport rollers 63, 64. In orderto turn off the drive motor 55 after the copy sheet has been set inmotion, an adjacent normally closed switch 135 having a feeler finger136 is provided to break the circuit of the switch 133. This turns oifthe drive motor until the tail of the copy sheet clears the switch 130at the ready position which then closes to advance a subsequent sheetinto the ready position.

In accordance with the present invention, means are provided forapplying electrostatic charges of unlike polarity to successive areas ofthe original as it is transported on the drum 30. More specifically inaccordance with the invention, the transport drum 30 is provided with aninsulating blanket of plastic or the like and charging devices arespaced at successive points about the periphery of the drum for applyingcharges of unlike polarity to renew and reverse the charge and thus toprevent the cumulative buildup of a charge of one polarity on thesurface of the blanket in successive cycles of rotation. As shown inFIGS. 5, 6 and 7, the first charging device, in the form of corona unit33, is connected to the positive terminal of the high voltage supply,while the second unit 35 is connected to the negative terminal. By wayof example, the positive voltage may be on the order of 5,000 voltspositive with respect to ground while the second charging device is5,000 volts negative. The insulating blanket 140 may, for example,consist of a Mylar, polypropylene, Teflon, nylon or the like, havinggood dielectric properties even under conditions of high humidity. Theblanket extends beyond the corners of the ridges (FIG. 2a) to avoid anyleakage of charge as a result of electrical stress.

In operation, when an original document is fed into the machine onto theinsulating blanket 140, and under the corona unit 33, positive chargesor ions created by the high positive charge on the wires 34 collect onthe surface of the sheet as shown in FIG. 6 and, since the originalunder normal atmospheric conditions is slightly conductive, some of thecharge will tend to migrate into the sheet to the interface between theoriginal and the surface of the blanket 140. Since the drum ispreferably grounded, either directly to the frame of the machine orthrough a resistor, corresponding negative charges will be induced atthe surface of the metal drum as shown. The mutual attraction betweenthe positive charges on, and in, the original, and the negative chargesin the drum itself, causes the original to tightly adhere to theinsulating blanket. The portions of the original which are subsequentlyexposed to the charging unit are similarly charged.

Subsequently when the leading edge of the original is advanced, bymovement of the drum, into the field of infiuence of 'the secondcharging device 35, the positive charges are neutralized and replaced bynegative charges from the negatively charged wires 36. The negativecharges on, and in, the original induce positive charges in the drumsurface on the opposite side of the insulating blanket. Any tendency forthe leading edge of the sheet to lift clear during the instant of chargereversal may be taken care of by providing a guiding edge 35a or thelike at 'the point of entry to the second charging unit 35 to maintainthe sheet close to the drum so that when the charge is reapplied theleading edge will snap back into seated position. A similar function isperformed by the guide surface 33a in unit 33 for recirculatedoriginals. Any momentary loss of attractive force in the successiveareas of the original being acted upon is of no consequence since thepredominant area of the sheet is still adherent. Moreover, theresistance of the average original is sufiiciently high so that Whilethe leading portion of the sheet may be negatively charged and theportion immediately following positively charged (see FIG. 7), there isno appreciable charge migration along the surface of the sheet.

Where the original is allowed to recirculate back to the first chargingdevice, as it is during the making of multiple copies, charge reversalagain takes place and a positive charge is reestablished as shown inFIG. 6. The charging and recharging with reversed polarity is repeatedas long as the original is allowed to recirculate.

I have observed that use of opposite polarity at the two chargingstations acting upon the same sheet provides 'a surprising improvementin the reliabilty of the electrostatic holding force, particularly wherethe drum is continuously cycled. The reason for this improvement may beexplained as follows: When there is no original on the blanket, whichoccurs when the machine is first turned on or when the drum is rotatingidly between usages, an electrostatic charge is applied directly to thesurface of the blanket. Moreover, while most of the drum area is coveredby the original during normal operation, the charge which is applied tothe original tends to migrate to the interface, i.e., to the outersurface of the insulating blanket and is augmented at each rotation ofthe drum. Thus where a single polarity is employed the insulatingblanket soon develops a steady high :level of charge which is of thesame polarity as the charge which is applied to the surface of theoriginal. Since the like charges repel, the net holding force thenbecomes a function of the difference in the charge applied to theoriginal and the charge which has accumulated on the surface of theblanket, which differential may be quite small, particularly underconditions of high humidity.

Where opposite polarities are used at the two charging stations,accumulation of charge during successive drum rotations is not onlycompletely overcome but a condition is produced at the original-blanketinterface which may actually augment the holding power of the chargeapplied to the face of the original. Taking first the case of aneworiginal, for example, when the machine is first put into operation,when a given area of the insulating blanket leaves the vicinity of thecharging unit 35, the residual charge on the surface of the blanket isnegative. Thus, when the surface is covered by an original 20 and fedinto the first charging unit 33, a positive charge deposited on, and in,the original is attracted not only by the induced negative charge in thedrum but also by the residual negative charge which may exist on thesurface of the blanket. During the time that it takes the original torotate from the first charging unit to the second, migration of chargewill normally occur in the sheet so that by the time the originalreaches the second unit the residual charge at the interface may beslightly positive. Such charge coacts with the negative charge appliedto the original at the second station to provide additional holdingforce. Where the original is not removed but is allowed to recirculatefor multiple copies, any residual charge on the blanket when the sameleaves the second charging station is negative. The charge on theoriginal is immediately neutralized and replaced by a positive chargewhen the surface of the original again enters the region of the firstcharging unit 33, with the residual tending, again, to augment theholding force. Thus, regardless of whether the original is new orrecirculated, the same conditions of charge and hold ing force existduring successive revolutions of the drum and there is uniformity offunction and result regardless of whether the original circulates onlyonce or a hundred times. On the contrary, securing the sheet tightly tothe drum not only insures uniformity of optical conditions in successiverevolutions but there is no possibility of the sheet skewing or shiftingwhich sometimes occurs during recirculation where other types of sheetholding means are employed.

While the invention has been discussed in connection with two chargingunits of opposite polarity, it will be apparent to one skilled in theart that the invention is not limited to use of two units and additionalunits may be employed such as that indicated in dot-dash outline at 33a(FIGS. 2 and 5). The unit 33a'may be positively charged in order toaugment the charge applied at the unit 33 or may be negatively chargedto augment the negative charge applied at unit 35. Still additionalcharging units may be used, provided only that there is at least onereversal of polarity per cycle of rotation of the drum.

Further, in accordance with the present invention means are provided forpre-curling the original prior to engagement with the drum 30 bystressing it beyond its elastic limit so that it acquires a set andtends more nearly to conform to the curvature of the drum surface. Inthe present instance such pre-curling is brought about by forcing theoriginal about a substantial portion of the periphery of a roller havinga curvature which greatly exceeds the curvature of the drum. Thus,referring to the roller assembly 25 shown in FIG. 8, the driven roller26 is in rolling engagement with idler rollers 27, 28 which are spaced,by angle a, about the periphery of the roller 26. The roller 26 isresiliently surfaced and has a nominal diameter which may be on theorder of of the diameter of the drum 30 with which it is used.Preferably the two rollers 27, 28 are resiliently surfaced and spaced todefine an are a of forced contact which is on the order of 75, i.e., anappreciable fraction of the total periphery. In any event, the radius rof the pre-curl roller 26 and the arc of forced contact are preferablychosen so that the resulting radius of curvature or set of the original,indicated at r in FIG. 8, is on the order of the radius of the curvatureof the drum itself. Thus the original tends, naturally, to conform tothe surface of the drum and the electrostatic forces need not be reliedupon to overcome any self-straightening effect in the original.

While it is true that the radius of curvature of the precurled original,indicated at r will apply to originals having average characteristics,for example, good quality letterhead, nevertheless it is found thatvariations on each side of the average tend to be self-compensating.Thus, in the case of originals of greater than average thickness thecurvature of the pre-curl will exceed the elastic limit to the extentthat the set radius may actually be less than the radius of curvature ofthe drum causing the original to cling intimately to the drum eventwithout electrostatic holding force. Conversely, where the original is athin tissue, the pre-curl roller may not be as effective to impart awell defined setto the original but, by the same token, a tissueconforms to the surface of the drum readily and with only a smallelectrostatic holding force even where it has no set whatever. Moreover,the precurl eifect brought about by a given set of pre-curling rollerstends to be self-compensating as regards wide variation in humidity.Thus, under dry conditions where a given original tends to be a littlestiffer or more elastic than usual resulting in a set of greater radius,i.e., less conforming, leakage of charge is reduced, resulting inaugmented electrostatic forces easily capable of maintaining theoriginal in secure contact with the drum. Conversely, where the humidityis high, accompanied by greater leakage of charge and slightly lowerelectrostatic forces, the original is more conformable and amenable toset and thus more easily held in place by the reduced electrostaticcharge.

It may be seen, therefore, that a given pre-curling setup, such as thatillustrated in the drawings, sufiices for a wide range of originals fromthinnest tissue to paperboard and over a broad range of humidity, fromarid to approaching saturation, permitting full utilization of theelectrostatic holding force in preventing creep or skew.

It is preferred to make the roller 27 of relatively small diameter andthe roller 28 of resilient material and of relatively large diameter.The latter thus tends to wipe the leading edge of the original reliablyinto the nip between the rollers 26, 28 even where the original fed intothe machine has an initial curvature which might cause it to miss thenip. Any one of the rollers may be driven but I prefer to drive theroller 26.

In general, it is found that the ironing effect of the expeller rollers22, 48 and the reverse curvature on the guides 49 is adequate tostraighten out a pre-curled origi nal after it is stripped from thesurface of the drum 30. L

However, where more complete straightening of the precurl is desired,and in accordance with one of the more detailed aspects of my invention,an uncurling roller assembly 25a (FIG. 9) may be used at the point ofexit from the drum 30 consisting of an uncurling roller 26a andcooperating rollers 22a, 28a. As in the case of the precurl roller 26,the arc of forced contact is indicated at a; however, the radius r ispreferably greater than that of roller 26 to avoid producing a set inthe opposite direc tion. Setting the radius to produce a fiat letterheadoriginal is a matter within the skill of the art. Either roller 26a or22a may be driven, whichever. is more convenient.

I have found that use of pre-curl combined with electrostatic adherenceto a transport drum results in a number of significant advantages. Inthe first place, it is found that a wide range of thickness of originalmay be accommodated with complete reliability, even up to paper board,with no tendency for the leading edge of the original to spring freeeven under conditions of extreme humidity or high leakage. Lowercharging voltages become possible. Then, too, the original tends toremain in contact with the transport drum even in the event that thesupply circuit is accidentally interrupted or inadvertently turned offwhile the original is in the machine. In the present machine turning onthe charging units after an interruption causes the holding forcebetween the original and the ground to be reestablished in the regionsof the charging units which is adequate to initiate movement, and theleading edge is kept sufficiently close to the drum so that it does notbecome hung up within the machine. Possible damage to the original orthe necessity for a service call is thus averted.

While the invention has been described above in connection with chargingunits of unlike polarity and at spaced positions around the periphery ofthe drum, and while this constitutes the preferred form of theinvention, attention is nevertheless directed to the alternativeembodiment shown in FIG. 10, in which unlike polarities are applied tothe successive areas of the original by switching between the terminalsof the power supply 75 as the drum is rotated and with the period ofswitching being so related to the period of rotation of the drum so thatthe same areas of the drum are not subjected repeatedly to the samepolarity of electrical charge. The switch 150, having contacts 151, 152is coupled to the drive motor by any means 153 capable of makingalternate contact. The switching produces alternating bands across theWidth of the original as shown.

In one of the aspects of the invention accumulation of charge on theinsulating blanket when using a single polarity may be avoided bycontacting the surface of the blanket with a grounded metal roller 155(FIG. 9). Such a roller extends the width of the drum and is biased inthe drums direction by any suitable means. Preferably the roller ispositioned between the stripping assembly and the first charging unit,permitting direct contact with the blanket between successive originals.If desired, the roller 155 may be replaced by a corona wire excited byhigh voltage A-C.

It has been convenient in the above discussion to speak in terms of anoriginal document fed into an ofiice photocopy machine. It will beapparent, however, to one skilled in the art that the invention is notlimited to transport of an original in the strict sense and that theterm original used in the following claims refers to any sheet of paperor the like requiring transport in fixed position with respect to thesurface of a rotating drum. Moreover, while a rigid, conducting drum ofcircular'section has been disclosed in the drawings, the term is notnecessarily limited to a circular drum but may include any equivalenttransport member, such as a belt, presenting an extensive gen erallycylindrical outer surface capable of electrostatically adhering thetransported sheet. Furthermore, it will be appreciated by one skilled inthe art that the present device is not limited to charging of the sheetby means of wires in the air, but would include equivalent chargingmeans, and hence the term corona unit shall be understood to be directedto sheet charging means generally. Finally, the term roller, applying inthe present instance to journaled cylindrical members, is notnecessarily limited to rotating elements and if desired, the undrivenone of a pair of rollers may consist of a polished rod.

I claim as my invention:

1. In an electrostatic photocopy machine or the like requiring transportof an original sheet alonga curved path of transport, the combinationcomprising a frame, a cylindrical drum grounded to and journalled in theframe and having means for driving the same, an insulating blanket onthe drum, means for feeding an original sheet to the drum for seatedtransport on the blanket, a first source of high charging voltage whichis of first polarity with respect to ground, a second source of highcharging voltage which is of second and opposite polarity with respectto ground, means for applying the voltages to the face of the originalsheet for causing the latter to seatingly adhere to the drum, saidvoltages being applied in such sequence that a given area on the surfaceof the blanket is alternately subjected to charges of first and secondpolarity thereby to avoid any tendency toward accumulation on thesurface of the blanket of a charge of one polarity incident tosuccessive cycles of rotation of the drum.

2. In an electrostatic photocopy machine or the like requiring transportof an original sheet along a curved path of transport, the combinationcomprising a frame, a cylindrical drum grounded to and journalled in theframe and having means for driving the same, an insulating blanket onthe drum, means for feeding an original sheet to the drum for seatedtransport on the blanket, a first source of high charging voltage whichis of first polarity with respect to ground, a second source of highcharging voltage which is of second and opposite polarity with respectto ground, means for applying the voltages of opposite polarity insequence to the face of the original sheet so that a given area of theoriginal sheet is first caused to acquire a charge of first polarityinducing a charge of second polarity in the adjacent region of the drumfor causing the document to seatingly adhere to the blanket as it istransported and so that said given area is shortly thereafter caused toacquire a charge of second polarity inducing a charge of first polarityin the adjacent region of the drum for causing the document to continueto adhere to the blanket and thereby to avoid any tendency towardaccumulation in the surface of the blanket of a charge of one polarityin successive cycles of rotation of the drum.

3. In an electrostatic photocopy machine or the like requiring transportof an original sheet along a curved path of transport, the combinationcomprising a frame, a cylindrical drum grounded to and journalled in theframe and having means for driving the same, an insulating blanket onthe drum, means for feeding an original sheet to the drum for seatedtransport on the blanket, a first source of high charging voltage whichis of first polarity with respect to ground, a second source of highcharging volt age which is of second and opposite polarity with respectto ground, means including a corona unit for applying voltage to theface of the original sheet for causing electrostatic adherence of thesheet to the drum, a switch for 10 alternately connecting the coronaunit first to one voltage source and then to the second voltage source,and means for continuously and automatically cycling the switch incidentto rotation of the drum to avoid any tendency toward accumulation in thesurface of the blanket of the charge of one polarity in successivecycles of rotation.

4. In an electrostatic photocopy machine or the like requiring thetransport of an origin-a1 sheet along a curved path of transport, thecombination comprising a frame, a cylindrical drum journalled in theframe and having means for driving the same, an insulating blanket onthe drum, means for feeding an original sheet to the drum for transportthereon, means for applying an electrostatic charge to the originalsheet for causing the same to adhere electrostatically to the drum, saidfeeding means including curling members for curlingly stressing theoriginal beyond its elastic limit and for imparting curvature thereto onthe order of the curvature of the drum to rnin1- mize restoring forcesin the original tending to restore the same to flat condition andthereby insuring maintenance of contact between the leading edge of theoriginal and the blanket over a wide range of electrostatic charge atthe leading edge.

5. In an electrostatic photocopy machine or the like requiring transportof an original sheet along a curved path, the combination comprising aframe, a cylindrical drum journalled in the frame and having means fordriving the same, an insulating blanket on the drum, means including apre-curling device for feeding the original to the drum so that theoriginal is conformingly seated on the blanket, a first charging deviceadjacent the pre-curling device for charging the face of the originalwith a charge of one polarity, a second charging device spaced from thefirst along the path of transport for dissipating the charge applied bythe first charging device and for applying to the face of the sheet anelectrostatic charge of opposite polarity, means for stripping theoriginal from the drum following circulation thereof, and dischargemeans inc-luding an uncurling device for stressing the original in theopposite direction for discharge from the machine in substantially flatcondition.

6. In an electrostatic photocopy machine or the like requiring transportof an original sheet along a curved path, the combination comprising aframe, a cylindrical drum journalled in the frame having means fordriving the same, an insulating blanket on the drum, a feed roller forfeeding a sheet to the drum for seated transport thereon, first andsecond rollers engaging the feed roller at spaced points about theperiphery of the feed roller, at least one of the rollers being powerdriven at a peripheral speed corresponding to the speed of the drum, thefeed roller having a diameter which is a minor fraction of the diameterof the drum and the first and second rollers being spaced about anappreciable are so that the original sheet fed between the feed rollerand the first and second rollers is stressed beyond its elastic limitresulting in a set of curvature which is in the direction of thecurvature of the drum for nesting of the sheet closely against thesurface of the drum thereby to minimize any tendency for the sheet tospring free self-restoringly from the surface at its leading andtrailing edges.

7. In an electrostatic photocopy machine or the like requiring transportof an original sheet along a curved path, the combination comprising aframe, a cylindrical drum journalled in the frame having means fordriving the same, an insulating blanket on the drum, a feed roller forfeeding a sheet to the drum for seated transport thereon, first andsecond rollers engaging the feed roller at spaced points about theperiphery of the feed roller, at least one of the rollers being powerdriven at a peripheral speed corresponding to the speed of the drum, thefeed roller having a diameter which is a minor fraction of the diameterof the drum and the first and second rollers being spaced at anappreciable are so that the original sheet fed between the feed rollerand the first and second rollers is stressed beyond its elastic limitresulting in a set of curvature which is in the direction of thecurvature of the drum for nesting of the original sheets closely againstthe surface of the drum, said second roller beinglarger than the firstroller or feed roller and surfaced to provide-a transverse wiping actionagainst the leading edge of the original so that the original is wipedinto the nip between the second roller and thefeed roller.

8. In an electrostatic photocopy machine or the like requiring transportof an original sheet along a curved path, the combination comprising aframe, a cylindrical drum joumalled in the frame having means fordriving the same, an insulating blanket on the drum, a roller forfeeding a sheet to the drum for seated transport thereon and having adiameter which is a minor fraction of the diameter of the drum, meansfor causing the sheet to conform to the curvature of the roller so thatthe sheet is curlingly stressed beyond its elastic limit resulting in aset of curvature which is in the direction of the curvature of the drumfor nesting of the sheet intimately against the surface of the drumthereby to minimize any tendency for the sheet to spring freeself-restoringly from the surface at its leading edge, and means forapplying an attractive force radially inward between the original andthe drum to prevent relative creep between the original and the blanketincident to multiple rotation of the original sheet on the drum.

9. In an electrostatic photocopy machine or the like for transport of anoriginal sheet along a curved path, the combination comprising a frame,a cylindrical drum journalled in the frame and having means for drivingthe same, means for feeding an original sheet to the drum for seatedtransport on the blanket, a charging device at the periphery of the drumfor applyingelectrostatic charge to the original sheet for causing thesame to adhere to 5 the drum, the drum being formed with a plurality ofperipheral grooves spaced side by side defining flat topped ridges,sheet-stripping means extending into the grooves and angling outwardlytherefrom for stripping the original sheet from the drum followingcompletion of a desired number of cycles of drum rotation, an insulatingblanket on the surface of the drum covering the flat topped ridges andextending beyond the corners thereof to prevent leakage of charge fromthe corners, and means at the surface of the drum for removing thecharge applied by the charging device thereby to prevent cumulativebuildup of charge on the surface of the blanket as a result ofsuccessive cycles of rotation of the drum.

References Cited 1 20 UNITED STATES PATENTS 287,957 11/1833 Osborne226-1 3,100,112 8/1963 Davis 271-53 3,172,657 3/1965 Brandt 271+51 OTHERREFERENCES Noel, N. G., IBM Technical Disclosure Bulletin, vol. 4, No.2, p. 27, July 1961, Capstan With Electrostatic Field Control.

1. IN AN ELECTROSTATIC PHOTOCOPY MACHINE OR THE LIKE REQUIRING TRANSPORTOF AN ORIGINAL SHEET ALONG A CURVED PATH OF TRANSPORT, THE COMBINATIONCOMPRISING A FRAME, A CYLINDRICAL DRUM GROUNDED TO AND JOURNALLED IN THEFRAME AND HAVING MEANS FOR DRIVING THE SAME, AN INSULATING BLANKET ONTHE DRUM, MEANS FOR FEEDING AN ORIGINAL SHEET TO THE DRUM FOR SEATEDTRANSPORT ON THE BLANKET, A FIRST SOURCE TO HIGH CHARGING VOLTAGE WHICHIS OF FIRST POLARITY WITH RESPECT TO GROUND, A SECOND SOURCE OF HIGHCHARGING VOLTAGE WHICH IS OF SECOND AND OPOSITE POLARITY WITH RESPECT TOGROUND, MEANS FOR APPLYING THE VOLTAGES TO THE FACE OF THE ORIGINALSHEET FOR CAUSING THE LATTER TO SEATINGLY ADHERE TO THE DRUM, SAIDVOLTAGES BEING APPLIED IN SUCH SEQUENCE THAT A GIVEN AREA ON THE SURFACEOF THE BLANKET IS ALTERNATELY SUBJECTED TO CHARGES OF FIRST AND SECONDPOLARITY THEREBY TO AVOID ANY TENDENCY TOWARD ACCUMULATION ON THESURFACE OF THE BLANKET OF A CHARGE OF ONE POLARITY INCIDENT TOSUCCESSIVE CYCLES OF ROTATION OF THE DRUM.